﻿134 BRITISH FOSSIL CEPHALOPODA. 



close to a specimen of this species and apparently broken from it, shows it small and 

 subcentral. The examples are usually small. 



Relations. — Portlock's Orthoceras incertum presents but few distinctive features, 

 and may well belong to the present species, as their author thought possible. 

 Authors have agreed that the Creseis Sedgwichii of Forbes is a synonym of this 

 species, but I have not discovered the original. The Orthoceras socium of Barrande 

 is, like our species, a widely spread one, both in time and space ; and though it 

 grows to be of larger size, and the septa are usually much more remote, the 

 ornaments are so similar that one can scarcely doubt that 0. subundulatum repre- 

 sents one of its varieties. The other species of the group with upward imbrications 

 are distinguished either by the greater obliquity of the ornaments or their want of 

 undulation. The minor peculiarities of ornament which have been described in the 

 type are not repeated in any of the other specimens, all of which are from Upper 

 Silurian, while the type is from the Lower. It is possible, therefore, that we may 

 be dealing with two distinct species, which can only be proved by better specimens 

 from the typical locality. 



Distribution. — In the Bala Series of Fermanagh (2) ; in the Wenlock Shale 

 of Wenlock (1), Barrington (4), Oernant (1), Builth (4), Garcoed, Usk (7), Llan- 

 badarn (1), Nantglyn (1), Llansannan (1), and Garragrena, co. Tipperary (1) ; in 

 the Coniston Flags of Horton (1) and Hawkshead (1) ; in the Coniston Grit, 

 Howgill (1); in the Denbigh Flags, Llangynyw (2) and Moel Seisiog (1); in 

 the Lower Ludlow of Ludlow (5 and 2 doubtful), Elton (1), Aymestry (1), 

 Ledbury (1) ; and in the Upper Ludlow of Ludlow (2). Also in the Upper 

 Silurian of Derrymore Glen, co. Kerry (2). 



The name of 0. subundulatum has been used for all species whose transverse 

 lineation had at all an undulating character, irrespective of whether they were 

 imbricating or not, and the recorded occurrences do not necessarily refer to our 

 present species. Thus it is stated by Wyatt-Edgell (Geol. Mag. iii. p. 161) to 

 occur in the Llandeilo Beds of South "Wales ; this may very probably mean a fine 

 variety of 0. Avelinii. It is recorded by M'Ooy from the Upper Bala, Ashgill, 

 Builth, and Dent ; and from Lower Silurian schists, Tirnaskea, Pomeroy : by Baily 

 from the same horizon at Kilmoksilla (Sheet 133) : by Davies from the Bala Beds, 

 Llanrwst : by Salter from the Upper Llandovery, Craighir, and three other localities, 

 — from the Wenlock Shale, Frid-y-fedwen and Capel-y-shiw ; from the Lower Ludlow, 

 Coalbrookdale ; from the Coniston Flags, Froshow Fell, Casterton Fell, and High 

 Hollins : by Harkness from Balmae, Kirkcudbright : by Brown and Henderson 

 from the Upper Silurian of the Pentlands ; from Blair Farm in the Catalogue of 

 Western Scottish Fossils : and by Baily from Upper Silurian rocks of Caherconree, 

 co. Kerry. 



